The present invention relates to an improved intermittent swirl type injection valve which is used for a fuel injection type internal combustion engine such as a diesel engine, and which swirls fuel with the aid of tangential passages and a swirl chamber so that the fuel is jetted substantially in conical form through a spray hole.
In a conventional intermittent swirl type injection valve of the same general type to which the invention pertains, a valve needle is slidably fitted in a valve hole formed in the valve body. There is unavoidably a certain gap between the wall of the valve hole and the cylindrical surface of the valve needle. In order to prevent leakage of pressurized fuel through the gap, heretofore, the gap has been formed by employing a design or manufacturing method in which the gap is made considerably small, typically 2 to 5 microns, or it is provided with a hydrodynamic arrangement. However, it is difficult to form a very small gap which is so small with a uniform accuracy.
Further, because the intermittent swirl type injection valve has a large spray angle, sometimes fuel droplets adhere to the wall of the combustion chamber or the intake manifold of the internal combustion engine. In order to overcome this adhesion, it is necessary to change the spray angle to a value suitable for the configuration or dimensions of the combustion chamber or intake manifold. However, the spray angle of the conventional intermittent swirl type injection valve cannot be readily changed to a desired value.
On the other hand, for the engine, it is required that the loss of energy in driving the injection pump be decreased, and, for a given quantity of injected fuel, the period of injection made as short as possible. Therefore, it is desirable to reduce the flow resistance in the spray hole or the fuel passage as much as possible, and accordingly it is not practical to reduce the diameter of the spray hole to an extremely small value.
The fuel is sprayed in the form of a cone having a cavity at the center. Foreign matter such as carbon particles may enter the spray hole through the cavity and clog the spray hole. Accordingly, it is necessary to prevent the entrance of foreign matter into the spray hole. However, it is practically impossible in the conventional intermittent swirl type injection valve to prevent the entrance of foreign matter into the spray hole.
In direct injection type internal combustion engines, the combustion chamber is formed by forming a recess in the top of the piston. Unlike an internal combustion engine with a swirl chamber and a precombustion chamber, this type of engine has no holes through which the chambers are communicated with the combustion chamber, resulting in a relatively low compression ratio. The direct injection type internal combustion engine is advantageous in that the engine has a smaller frictional loss and lower fuel consumption. Thus, such an engine has been extensively employed as a large engine.
On the other hand, a small engine having cylinders of a small diameter is disadvantageous in the formation of the mixture gas when compared with a large engine.
In a conventional direct injection type internal combustion engine, a fuel injection valve, directed substantially towards the center of the recess formed in the top of the piston, jets or sprays a plurality of spray streams radially from a plurality of spray holes. With this arrangement, an intake vortex formed by the intake valve and the intake passage during the intake operation of the engine is present even at the end of the compression stroke, and therefore mixture gas is formed while the fuel spray streams are being pulled in the swirling direction of the vortex in the recess. The diameter of the recess is generally 40 to 70% of the diameter of the piston or the cylinder. Accordingly, in a small engine in which the piston's diameter is 100 mm or smaller, the diameter of the recess is small, and hence the compression ratio cannot be significantly increased without decreasing the diameter of the recess. Thus, the engine suffers from the difficulty that the fuel spray streams jetted or sprayed radially from the spray holes of the fuel injection valve strike the inner wall of the recess, forming a film thereon or remaining as large droplets. As a result, the fuel is not effectively burned. In other words, the quantity of mixture gas available for combustion is decreased so that the engine output is decreased while the fuel consumption is increased. Moreover, the engine may smoke.
In order to eliminate these difficulties, it has been proposed to use a swirl type injection valve whose penetration force is sufficiently small that no fuel spray strikes the inner wall of the recess. However, in a swirl type injection valve fabricated according to a conventional design and manufacturing method, the spray angle is considerably large. Therefore, although the spray does not strike the wall of the combustion chamber, it has a tendency to stick to the top of the piston. In addition, the penetration force of the spray is extremely small, and therefore the fuel droplets may not move far in the combustion chamber.
Fuel droplets which stop moving in the combustion chamber are not burned because of being enveloped in combustion gas. Accordingly, it is necessary for the fuel droplets to have a momentum sufficiently large to move in the combustion chamber until they are burned. Therefore, the direct injection type internal combustion engine should use a swirl type injection valve whose spray angle is 75.degree. or smaller. A design and method of manufacturing such a swirl type injection valve having such a small spray angle have not yet been realized.